Determination of $GL(3)$ Hecke-Maass forms from twisted central values

Suppose ${\pi }_1$ and ${\pi }_2$ are two Hecke-Maass cusp forms for $SL(3,\mathbb{Z})$ such that for all primitive character $\chi$ we have $$L(\frac{1}{2},{\pi }_1\otimes \chi )=L(\frac{1}{2},{\pi }_2\otimes \chi )\mathrm{.}$$ Then we show that ${\pi }_1={\pi }_2$.